1. Field of the Invention
The present invention relates to image projection systems. More specifically, the present invention relates to liquid crystal light valve image projection systems.
While the present invention is described herein with reference to illustrative embodiments for a particular application, the invention is not limited thereto. Those of ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope thereof.
2. Description of the Related Art
The development of the liquid crystal light valve has opened the door to substantial progress in the state of the art of high quality large screen projectors. The reflective mode liquid crystal light valve is a thin film, multilayer structure comprising a liquid crystal layer, a dielectric mirror, a light blocking layer, and a photoresponsive layer sandwiched between two transparent electrodes. A polarized projection beam is directed through the liquid crystal layer to the dielectric mirror. An input image of low intensity light, such as that generated by a cathode ray tube (CRT) is applied to the photoresponsive layer thereby switching the electric field across the electrodes from the photoresponsive layer onto the liquid crystal layer to activate the liquid crystal. Linearly polarized projection light passing through the liquid crystal layer and reflecting from the dielectric mirrors is polarization-modulated in according with the information incident on the photoconductor. Therefore, when a complex distribution of light, for example, a high resolution input image, is focused onto the photoconductor surface, the device converts the image into a replica which can be projected with magnification to produce a high brightness image on a viewing screen. U.S. Pat. No. 4,019,807, issued to D. D. Boswell et al on Apr. 26, 1977, disclosed such a high performance reflective mode liquid crystal light valve.
A graphics display projector using a liquid crystal light valve of the above-type is described in an article entitled "Application of the Liquid Crystal Light Valve to a Large Screen Graphics Display", published in the 1979 Society for Information Display (SID), International Symposium, Digest of Technical Papers, May 1979, pp. 22-23.
More sophisticated liquid crystal light valve image projection systems are illustrated in the following patents: U.S. Pat. No. 4,425,028, issued to R. J. Gagnon et al on Jan. 10, 1984; U.S. Pat. No. 4,461,542, to R. J. Gagnon on July 24, 1984; and U.S. Pat. No. 4,464,019, issued to R. J. Gagnon on Aug. 7, 1984.
These designs provide high resolution, high contrast full color images by separating an input beam into different optical paths for polarization and/or color processing. The beams are then recombined at or prior to illumination of a main polarizing prism.
These designs also illustrate the continuing effort in the art to provide high performance, low cost image projection with a compact assembly. For example, while the system of U.S. Pat. No. 4,461,542 provides a less bulky, more compact design than that of U.S. Pat. No. 4,464,019, it requires two projection lenses to output the display information. And while the system of U.S. Pat. No. 4,425,028 provides a compact design requiring a single projection lense, it has been recognized that the packagability of the system could be improved further by locating the light valve CRT assemblies in a parallel coplanar relation. Thus, a need remains in the art for a compact full color high performance liquid crystal light valve image projection system.